The Finns Children Of Bodom have called off their appearance at next summer's Tuska Open Air in Helsinki, Finland. This time, however, it has nothing to do with Alexi Laiho. The band will give priority to a big US tour.

The band's bassist Henkka "T. Blacksmith" explained: "We've been waiting to play Tuska for some years now. It is our home festival after all. Unfortunately this year we have to sacrifice a couple of festivals in Europe in order to be able to be part of a big tour in USA. These are not easy nor nice decisions. We only can hope we can do Tuska in the near future again. Please stay tuned for our schedules for summer 2013. Fortunately we are able to play shows in Europe as well. Looking forward!"

Why not? What if Wintersun was playing later than them and they got pissed?

That's impossible
COB are around since the '90s, Wintersun since 2004 and the former had released 7 album, the latter just 2; COB have a really greater number of fans than WS.
Business is business...

Exactly, there's no way WS would be later than COB. IMO this has nothing to do with timeslot. But if they had a big tour including, i don't know let's say 25 shows, and if they stayed in Europe they would have had 10 ... Easy, but unpleasant decision. Plus they are also very popular in the US so the venues are going to be full anyway. And maybe they had a greater cashback on US shows than on Fests, that's for sure.